In an LTE (including LTE-Advanced) system, UE categories on capability of the user apparatus UE are defined, and requirements that should be supported are defined for each UE category. For example, the total number of soft channel bits, and the number of supported MIMO layers and the like are defined for each UE category (non-patent document 1).
Also, in LTE, it is defined that the user apparatus UE reports a UE category of the user apparatus UE itself to the base station eNB by a predetermined message “UE-EUTRA-Capability” (non-patent document 2).
In release 8 (Rel-8, hereinafter) of 3GPP, a field for reporting UE categories 1˜5 is defined in the message of UE-EUTRA-Capability. From release (Rel-10, hereinafter), values of UE category 6 and after 6 are additionally defined, so that a field for reporting that is defined. More specifically, for example, in an information element (IE) of UE-EUTRA-Capability shown in FIG. 1, a field for reporting UE categories 1˜5 and a field for reporting UE categories 6˜8 are defined as indicated by underlines.
Also, in LTE, various Transmission Modes (transmission modes, described as TM hereinafter) that determines a transmission scheme of data (PDSCH) from the base station eNB to the user apparatus UE are defined, so that the user apparatus UE performs data reception operation according to the TM configured from the base station eNB (non-patent document 3). For example, TM3 indicates open loop spatial multiplexing and TM4 indicates closed loop spatial multiplexing. Feedback of an RI (rank number) from the user apparatus UE to the base station eNB is necessary for both of them.
Also, in the user apparatus UE and the base station eNB of LTE, in an HARQ entity of an MAC (Media Access Control) layer, HARQ (Hybrid ARQ) control is performed. For example, in HARQ control for downlink data in the user apparatus UE, when decoding of downlink data (TB: transport block) succeeds, the user apparatus UE returns ACK to the base station eNB. When decoding fails, the user apparatus UE returns NACK to the base station eNB. Accordingly, in HARQ, retransmission control is performed by transmitting ACK/NACK. In HARQ, when the user apparatus UE fails in decoding of received data (when data is erroneous), the user apparatus UE holds the data, combines data retransmitted from the base station eNB and the held data, and decodes the combined data. Accordingly, strong tolerance against errors is provided. A storage unit for holding the data (memory area) is called a soft buffer.